Angular dependence of detector responses in high-energy brachytherapy

Area of Science:

• Medical Physics
• Radiation Dosimetry
• Brachytherapy

Background:

• Accurate dose measurement is critical in brachytherapy.
• Detector response can be influenced by angular dependence, especially in complex radiation fields.
• Understanding these effects is crucial for precise Ir-192 dosimetry.

Purpose of the Study:

• To characterize the angular dependent response of ionization chambers and a diamond detector.
• To investigate the influence of medium (air vs. water) and distance on detector response.
• To evaluate detector performance under Ir-192 irradiation conditions.

Main Methods:

• Monte Carlo (MC) simulations and experimental measurements were performed.
• Detectors were rotated relative to the Ir-192 beam axis at various distances in air and water.
• Detector-specific properties like dead volumes and asymmetries were considered.

Main Results:

• Angular dependence was <0.5% for rotations up to 50° in water at 10 cm.
• In air, deviations exceeded 0.5% at smaller angles for some detectors.
• Volume averaging and surrounding high-Z materials significantly influenced angular response, especially near the source.

Conclusions:

• This study provides the first investigation of perturbation factors affecting angular detector response in brachytherapy.
• Results are vital for estimating angular-dependent responses in complex dosimetry scenarios.
• Findings aid in improving dose rate distribution measurements with multiple sources or heterogeneous environments.